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Optimization of SIS100 Lattice and Dedicated Collimation System P. Spiller, GSI ICFA 2004

Optimization of SIS100 Lattice and Dedicated Collimation System P. Spiller, GSI ICFA 2004 Bensheim 18.10.04. Lattice Optimization - General. CDR triplet lattice with 4 dipoles per cell (Acceptance : 100 x 55 mm mrad).

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Optimization of SIS100 Lattice and Dedicated Collimation System P. Spiller, GSI ICFA 2004

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  1. Optimization of SIS100 Lattice and Dedicated Collimation System P. Spiller, GSI ICFA 2004 Bensheim 18.10.04

  2. Lattice Optimization - General CDR triplet lattice with 4 dipoles per cell (Acceptance : 100 x 55 mm mrad) Doublet lattice with 2 dipoles per cell (Acceptance : 170 x 50 mm mrad ) • Maximum beam acceptance („small“ aperture magnets for fast ramping) • Dispersion free straight sections (no transv.-longit. coupling in rf systems) • Low dispersion in the arcs (momentum spread during compression) Dx = 2.5 m • Six superperiods (space for large tune spread and long storage time)

  3. U28+ : Reference Ion of the FAIR Project Present Intensity in SIS12/18 2.5 x 109 U73+ -ions /cycle Planned Intensity in SIS12 Booster Operation 2.5 x 1011U28+ -ions /cycle Planned Intensity in SIS100/300 1 x 1012 U28+ -ions /cycle The step to highest heavy ion beam intensities requires medium charge states.

  4. History of U28+ operation at GSI • <2001 Life time measurements at low intensities (108) • 2001 First observations of time dependend life time and fast pressure variations within single SIS18 cycles • 2002/2003 Proposal and installation of a dedicated collimator for the controle of desorption gases in SIS18 • 2003 Report on analysis and first modelling of the observations • 2003/2004 Desorption rate measurements at the GSI test stand • 2004 Optimization off SIS100/300 lattice structure with respect to collimation efficiency • 2004 First time dependend modelling including primary losses, collimation efficiency, pumping properties, target and projectile (mulitple) ionization and desorption

  5. Life Time and Vacuum Instability Beam losses induced by a dynamic vacuum or a vacuum instability is the most crucial item for achieving the goals of the new facility.

  6. Residual Gas Pressure Dynamics Fast variations (time scale s) Slow variations (time scale s)

  7. Vacuum Stabilization – General • Short cycle time and short sequences SIS12 :10 T/s - SIS100 : 4 T/s (new network connection in preparation) • Enhanced pumping power, optimized spectrum (Actively cooled magnet chambers 4.5 K, NEG coating (local and distributed) • Localization of losses and controle of desorption gases Prototype desorption collimator installed in S12 • Low-desorption rate materials Desorption rate test stand in operation cryo pump increased pressure ion beam wedge collimator

  8. Loss Mechanisms

  9. Design Concept for Medium Charge State Uranium Beams 1 1. From all loss mechanisms, only particles which are further stripped by collisions with the residual gas atoms are able to reach the beam pipe within one lattice cell ! Each lattice cell must be designed as a charge separator. The „stripped“ beam (U29+) must be well separated from the reference beam. The low dispersion function in the SIS100 arcs complicate this issue. 3. The main lattice structure optimization criteria is the collimation efficiency for U29+-ions. No additional load for the UHV system during beam operation

  10. Design Concept for Medium Charge State Uranium Beams 2 The collimation efficiency for U29+ - ions must be 100%. Mainly single (no multiple) ionized ions shall be generated. The 100% collimation efficiency must be achieved with collimators at maximum distance from the beam edge. No significant acceptance reduction shall be caused by the collimator system. 7. No ionization beam losses shall occure on cold and NEG coated surfaces. 8. By an optimued design, the effective desorption rate of the collimators shall be almost zero.

  11. SIS18 Prototype Desorption Collimator Wedge collimator + secondary chamber + cryo pump Desorption gases are generated in secondary chamber The collimation system must controle the desorption gases (eff = 0)

  12. SIS18 experimental LEAR P = 3.67x10-11 P = 2.87x10-11 H2 – 81.87 % CH4 – 11.86 % CO – 3.02 % Ar – 3.25 % H2 – 83.18 % He – 2.36 % CH4 – 10.38 % CO – 1.73 % N2 – 1.38 % Ar – 0.97 % Multiple Ionisation Average number of proj. loss electrons R. Olsen et.al., HIF04 SIS18 injection energy SIS100 injection energy E [MeV/u] Multiple ionization reduces the collimation efficiency Cross section interpolation

  13. Charge Separator Lattice and Collimation wedge collimator at 80 K cold, pumping secondary chamber at 4.5 K About 10 collimators per arc

  14. Collimation Efficiency coll = Ncoll/Ntotal at injection energy

  15. Storage Mode Lattice Collimation efficiency Collimator distance from beam axis SIS100 Lattice

  16. Lattice Choice and Optimization

  17. Simulation Code Development • Integrated time resolved loss and pressure calculation must comprise: • Initial residual gas composition • Initial systematic beam losses (e.g. multi turn injection) • Projectile and target ionization cross sections and resulting ionization degree and multiple ionization degree • Collimation efficiency for the generated ionization degrees • Effective desorption rate of the collimation system • Realistic pumping power for the different residual gas consitutents and UHV conductivity • Desorption coefficients and assumptions for the desorped masses. • Desorption created by target ionization.

  18. Time Resolved Simulation of Losses and Pressure N, p[mbar] t [s] t [s] First step: Evaluation of a single SIS18 cycle Second step: Evaluation of a high repetition mode (booster) Recent results indicate the importance of initial losses (MTI)

  19. (Present ) Limits of the Concept • The collimation system is designed for uranium operation. • The collimation efficiency for other ion species is lower (lower max. intensity). • Some amount of additional pressure load can not be avoided. • Therefore chambers of the s.c. magnets shall be cold and act as cryopumps. ( Without active cooling, the dipole chamber temperature was about 50K. ) • Cooling channels must be foreseen at least in the drift- and quadrupole chambers. • ( about 700 m of the chambers will be cold and act as cryo pumps ) • NEG coating of SIS100/300 magnet chambers is not possible since baking would be required. • NEG coating will be considered for the straight drift chambers (200 m).

  20. Summary • A promising concept for the high current U28+ operation has been developed. • The situation of the SIS12 booster operation is more critical since the lattice • is not optimized for collimation and multiple ionization is more probable. • The collimation efficiency for other heavy (e.g. Au, Pb) ions is lower and the • fractions of the beam which may be lost uncontrolled is higher. • 4. The ionisation cross section drop for lighter ions and life time is longer.

  21. Acknowledgements: group BEN and project group SIS100/300

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